A nebulizer is commonly used in respiratory therapy and in medical research to dispense an aerosol. Atomization of the aerosol occurs as pressurized air is fed into the bottom of the nebulizer bowl. The patient inhales through an outlet orifice at the top of the nebulizer. This forces the aerosol into the respiratory system. It is customary to regulate the time interval of the pressurized air flow with each breath. Short timed bursts of pressurized air are used to atomize the liquid in the nebulizer. The dosimeter shuts off the air flow at predetermined times after each inhalation. When the pressurized air is shut off, no further atomization of the liquid occurs. Then the patient only breathes ambient air which enters through the ambient air inlet at the top of the nebulizer.
It is well understood that each breath of a patient varies in volume and inspiratory flow rate. The nebulizer has an ambient air entrance at the top to accommodate the patient's requirement for air. In operation when a patient inhales with great force, he could inhale all the atomized aerosol in the nebulizer. There traditionally exists an unregulated direct flow of air from the ambient entrance into the patient through the ambient entrance.
However, during weak inspiratory efforts the patient may inhale the atomized aerosol slowly or alternatively, after a strong inspiratory effort the aerosol may enter the respiratory tract at a higher flow rate. Slow inhalation of the aerosol is generally desired in order to allow the aerosolized drug to penetrate deeper into the respiratory tree.
Patients using the above system cannot self-regulate their own inspiratory flow rates. Therefore, wide ranges of inspiratory flow rates for each breath are to be expected. This can create an inconsistent administration of aerosol to the respiratory tree.
Thus, it is desirable to provide a constant output flow rate of atomized drugs regardless of variations in inhalation pressures. The present invention greatly enhances the reproducibility and constancy of the output flow rate of atomized aerosol from a nebulizer by introducing a variable diameter input valve in the ambient entrance. The diameter of the valve reduces increased suction pressure caused by inhalation.
In operation the variable diameter input valve reduces its orifice size by means of collapsing flexible walls. The pressure inside the nebulizer drops in proportion to the patient's inhalation force. The valve's flexible walls collapse in proportion to the pressure differential between ambient and nebulizer chamber pressures. Thus, during strong inspiratory efforts the valve's flexible walls collapse. A smaller input orifice is formed, thereby causing the flow rate of the ambient intake air to remain constant. It is understood that the flow rate of the ambient intake air is the same as the flow rate of the patient's inhalation. This flow rate is the nebulizer's throughput flow rate. A higher velocity reduced volume of air through a narrow orifice is formed while the nebulizer's throughput flow rate remains constant. In the opposite situation the patient performs a weak inspiratory effort. This results in the valve's flexible walls remaining open. A slower but higher volume of ambient air passes through the wider orifice. Overall within the normal limits of human breathing variations, the nebulizer's throughput flow rate through the valve's flexible walls remains constant. The analogous situation would be for a patient to first suck very hard through a tiny straw for three seconds and getting 1000 droplets of medicine. Next the patient would suck very lightly through a wide straw for three seconds and get 1000 droplets of medicine. The result is that the patient inhales his medication at the same rate regardless of how hard he inhales. When the valve is employed with the dosimeter the nebulizer can be configured such that the inspiratory flow rate and the time interval of inspiration is fixed. This enables the operator to characterize the nebulizer under such conditions such that the output of aerosol is consistent from discharge to discharge. When the nebulizer is calibrated by weighing before and after discharge the exact amount of aerosol administered is determined. Selected amounts of aerosolized drug may then be given by adjusting the concentration of drug in the nebulizer accordingly.